Heat exchangers are devices used for the transfer of heat between two or more media. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. Heat exchangers are used in many mechanical systems, including heating, ventilation, and air conditioning (HVAC) systems.
The term HVAC (heating, ventilation, and air conditioning) generally refers to mechanical systems relating to indoor or automotive environmental comfort. HVAC systems are generally configured based on principles of thermodynamics, fluid mechanics, and heat transfer. Such mechanical systems typically include components such as ducts or pipes, pumps, valves and vents, and heat exchanger devices. Pumps are frequently used in order to transport a fluid from one place to another against forces exerted on the fluid, and heat exchangers are often used to transfer heat between multiple mediums. For example, in an HVAC system air circulates throughout the building envelope and is conditioned (heated, cooled, purified, etc.) as needed. Air ducts may be installed throughout the interior space of a building to move the air and to supply the conditioned air to a room (via outlet vents). Return ducts may be used to remove air (via return-air grilles) and direct the air to a heat exchanger device, where heat is either put into the system or extracted from the system to be dissipated into the exterior environment (e.g. outside of the building envelope).
In addition to being used for heating, refrigeration, and air conditioning, heat exchangers may be used in power plants, chemical plants, petroleum refineries, natural gas processing, and sewage treatment. Heat exchangers of varying scales and complexities may be implemented in mechanical devices and systems that require heat transfer. For example, a heat exchanger would typically be found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils to cool the coolant and heat the incoming air. Examples of systems where heat dissipation would be desirable are various electro-mechanical systems, and electronics applications such as conventional computing systems. In a typical computing system which includes a CPU, one or more memory devices, and other circuitry, cooling of the CPU in particular may be an important design consideration.